The present invention relates to a structure for attaching an urging member, such as a coil spring, to an attachment member via a bushing.
Japanese Laid-Open Patent Publication No. 2009-142484 discloses a structure for attaching a metal back spring to a metal frame embedded in the seat back of a vehicle seat. The attachment structure includes a plastic bushing, which is arranged in the frame having an insertion hole. The back spring is attached to the frame via the bushing.
Other conventional attachment structures for urging members include, for example, the structure illustrated in FIGS. 20 and 21. In this attachment structure, as illustrated in FIG. 20, an attached portion 111 of an urging member 110 is inserted in an insertion hole 101 formed in a plate-like attachment member 100. The urging member 110 is thus attached to the attachment member 100. A bushing 120 is attached to the insertion hole 101. The bushing 120 includes a first bushing forming member 121 and a second bushing forming member 122.
With reference to FIG. 20, the first bushing forming member 121 includes a first cylindrical portion 121a and a flange portion. The first cylindrical portion 121a is press-fitted into the insertion hole 101 of the attachment member 100 from below as viewed in FIG. 20. The flange portion extends from the basal end (the lower end portion as viewed in the drawing) of the first cylindrical portion 121a. The second bushing forming member 122 has a second cylindrical portion 122a and a flange portion 122b. The second cylindrical portion 122a is fitted into the inner space of the first cylindrical portion 121a from above the attachment member 100 (from above as viewed in FIG. 20). The flange portion 122b extends from the basal end (the upper end portion as viewed in the drawing) of the second cylindrical portion 122a. As illustrated in FIG. 21, a plurality of through holes 122c are formed and arranged circumferentially at the radially inner side of the flange portion 122b, which is connected to the second cylindrical portion 122a. 
Referring to FIG. 20, the attached portion 111 of the urging member 110 is inserted into the inner side of the second cylindrical portion 122a. Since the attached portion 111 is bent, the attached portion 111 contacts inner side surfaces of opposite axial ends of the second cylindrical portion 122a. 
In the attachment structure illustrated in FIGS. 20 and 21, an excessive load applied to the bushing 120 by the urging member 110 may deform contact sections 123, each of which is a section of the second bushing forming member 122 that contacts the attached portion 111 of the urging member 110. For example, as illustrated in FIG. 21, the attached portion 111 may contact the inner circumferential surface of the basal end of the second cylindrical portion 122a and one of the insertion holes 122c may be located radially outward of the contact sections 123. In this case, if an excessive load is applied to one of the contact sections 123 by the attached portion 111, the load of the attached portion 111 deforms the contact section 123 radially outward, thus causing the attached portion 111 to bite into the second bushing forming member 122. In this state, when the attached portion 111 moves in the direction represented by the arrow of a broken line in FIG. 21, the force produced by such movement of the attached portion 111 may act on the second bushing forming member 122, thus causing the bushing 120 to co-rotate with the attached portion 111. This may cause the bushing 120 to slide on the attachment member 100, thus generating noise from such sliding.